Various micropuncture studies in rats are proposed in an effort to obtain information leading to a better understanding of the mechanisms and control of glomerular filtration and tubular transport in health and disease. Specific projects are: (1) Studies of glomerular ultrafiltration dynamics to determine those circumstances under which filtration equilibrium occurs, the extent of plasma flow dependency and the intra-renal sites of vascular resistance; (2) Studies in experimental heart failure resulting from aortic-caval shunt to determine tubular locus and mechanisms responsible for retention of salt and water during the development and maintenance of congestive heart failure; (3) Renal function in spontaneously hypertensive rats, characterization of their salt excretion, and relation to the hypertensive state; (4) Pathophysiology of acute renal failure with particular reference to the mechanisms responsible for oliguria; (5) Individual nephron function in rats with immunologically induced tubular disease; (6) Neural influences on renal function, including the effects of acute and chronic denervation, alpha and beta adrenergic drugs and renal nerve stimulation; (7) Calcium transport, with attention to the interaction between calcium and sodium transport and the effects of parathyroid hormone; (8) Urate excretion, to localize and quantitate tubular transport of urate under normal conditions, in rats with reduced renal mass and following administration of various drugs known to influence urate excretion; (9) Urea transport to determine whether its transport is entirely passive or in part carrier-mediated.